Greenhouse Buying Guide: How to Choose the Right Size, Material and Base

Glass, Polycarbonate or Plastic Film — Which Material Should You Choose?

Almost every greenhouse on the market is glazed with one of three main materials. The differences come down to light transmission, insulation, weight, durability and price — there's no single "best," only what fits your situation.

Glass

Glass lets in the most light and essentially doesn't age — a glass greenhouse from the 1960s can still perform beautifully if the frame has been kept up. The tradeoff is weight: glass needs a sturdy, well-anchored frame and a solid foundation, or panes crack the moment the structure settles unevenly. Glass is also vulnerable to hail and falling branches, and individual panes sometimes need replacing after a storm.

Polycarbonate (twin-wall)

Twin-wall or triple-wall polycarbonate traps air between layers, which is why it insulates better than single-pane glass despite weighing less. It flexes instead of shattering, which makes it the safer choice if kids play nearby, hail is common where you live, or a branch could plausibly land on the roof. Light transmission is somewhat lower than glass, but still plenty for most vegetables and seedlings. This is the material most home greenhouses use today, and it's rarely the wrong call if you're unsure.

Plastic film / hoop houses

A hoop house stretches a thin plastic sheet over a bent steel or aluminum frame. It's by far the cheapest option per square foot and can go up in a weekend, but the film breaks down under UV exposure and typically needs replacing every few seasons, depending on quality and exposure. A hoop house is a reasonable way to find out whether a greenhouse actually suits your growing habits before committing to something permanent, or as extra seasonal space alongside a smaller main greenhouse.

Good to know. Not sure which to pick? Polycarbonate at least 6mm thick is the safest compromise for most gardeners — insulating enough to meaningfully extend your season, tough enough that you won't lie awake worrying about a cracked panel.

Aluminum, Wood or Steel — Which Frame Should You Choose?

Glazing gets most of the attention, but the frame holding it together matters just as much for how long the greenhouse lasts and how much upkeep it needs.

Aluminum

Aluminum is the most common frame material in modern kits. It's light, doesn't rust, and needs essentially no maintenance beyond keeping it clean. The tradeoff is that aluminum conducts heat away faster than timber, which can create condensation and cold spots where the frame meets the glazing if the design isn't well thought out.

Wood (often cedar or pressure-treated lumber)

A timber frame insulates better at the frame itself, and many gardeners simply find it more attractive, especially in an older garden or close to the house. It needs more upkeep — bare wood needs oiling or repainting every few years — and typically costs more than an equivalent aluminum frame. Cedar handles moisture better than most woods left untreated, but it's also the priciest option.

Steel

Steel shows up mostly in larger production and tunnel-style greenhouses rather than smaller hobby kits. It's strong and handles heavy snow loads well, but untreated steel rusts once the surface coating is damaged, so galvanized or powder-coated steel is worth insisting on if you're considering it.

Good to know. Whatever the frame material, ask whether it's galvanized or otherwise coated. An untreated or poorly protected aluminum fitting can corrode almost as badly as steel if it's exposed to salt air or persistent damp.

What Size Greenhouse Do You Actually Need?

Almost everyone who buys their first greenhouse wishes, a year later, that they'd gone one size up. It's easy to underestimate how much floor space benches, pots and walking room actually take, and easy to overestimate how little you'll need.

A width of at least 6 ft (1.8 m) gives you room to turn around and run a bench along one long side. Want benches or growing beds on both sides with a path down the middle? Plan on at least 8 ft (2.4 m) of width. Eave height should be at least 5 ft (1.5 m) so light still reaches the edges properly, and more if you're growing tall crops like tomatoes that quickly reach the roof.

Also think about what you're actually growing. If you're starting tomatoes, peppers and cucumbers from seed early in the season on a sowing calendar, trays and pots on shelving take up far more floor space than you'd expect before everything moves outdoors.

Where Should a Greenhouse Go in Your Yard?

Siting affects how much use you actually get out of a greenhouse more than almost any other decision in this guide. A greenhouse tucked in the shade of a tree will underperform a smaller one in full sun.

Facing the long side south or southwest gives the most sun through the day and is the best general rule of thumb, but it isn't a dealbreaker if your only open spot faces another direction — a greenhouse that gets strong morning and midday sun still beats no greenhouse at all.

Avoid siting it directly under trees. Beyond the shade, you're risking falling branches on the roof and leaves clogging vents and gutters every autumn.

Leave room to walk all the way around the structure for maintenance, glass cleaning or repainting the frame. A couple of feet of clearance on every side is a reasonable minimum.

On an exposed site, think about your prevailing wind direction. Facing a gable end into it puts less strain on the structure than exposing a full side wall.

Proximity to a water spigot makes watering far easier, especially if you're hand-watering through summer. If you plan to run power for a fan, heater or automatic vent opener, plan the wiring before the foundation goes in — it's much easier than digging things up afterward.

Common mistake. Putting the greenhouse wherever there happens to be open space, instead of wherever the sun actually reaches. Move the compost bin or the bike shed instead of compromising on light.

Freestanding or Lean-To Greenhouse?

Most home greenhouses are freestanding, but a lean-to model built against a south-facing wall has real advantages that are easy to overlook.

A lean-to greenhouse benefits from the wall's stored heat, which evens out nighttime temperatures and can stretch the growing season a bit further than a freestanding structure of the same size. It's also usually closer to power and water, which simplifies running both. The downside is that you only get light and ventilation from three sides instead of four, and the greenhouse becomes permanently tied to that wall rather than something you could relocate later.

A freestanding greenhouse gets full light from every direction and can go wherever the sun is actually best, regardless of where the house sits. It's also the natural choice if you've already settled on an open spot in the yard, say next to a raised bed or vegetable patch.

Which Foundation Suits Your Greenhouse?

The foundation barely shows once the greenhouse is up, but it matters more than most people assume — both for how stable the structure is and how even the temperature stays inside.

If the greenhouse will stay up year-round and you want to start growing early in spring, an insulated slab or an insulated pier foundation is time well spent. For a smaller hoop house that mostly extends the summer season, a bed of compacted gravel is usually enough to keep weeds down and drainage decent.

Your climate zone matters here too:

Good to know. Whichever base you choose, grade the ground so it slopes gently away from the greenhouse, never toward it. Otherwise rainwater runs straight under the walls, and you're dealing with damp and mold by the first fall.

Do You Need a Permit for a Greenhouse?

Rules vary widely by state, province and municipality, but there are some common patterns worth knowing before you buy.

In much of the United States, detached accessory structures under roughly 120–200 sq ft are often exempt from a building permit under model codes like the International Residential Code, though many local jurisdictions set their own, sometimes stricter, threshold. In Canada, structures under about 100–110 sq ft (roughly 10 m²) are commonly exempt, though this varies by city and province as well. Exemptions typically assume a freestanding, unheated structure with no plumbing or electrical connections — adding power or water for a fan, heater or irrigation system often triggers permit requirements even for a small greenhouse.

None of this is a substitute for checking locally. Zoning, setback rules and permit thresholds are set at the city or county level and can differ significantly even between neighboring towns.

Good to know. A five-minute call to your local building or planning department before you order is far cheaper than finding out afterward that your new greenhouse needs to be relocated or torn down.

Ventilation and Shading — Keeping It From Overheating

A greenhouse without enough ventilation can turn uncomfortably hot on a moderately sunny spring day, long before summer arrives. Interior temperatures can climb faster than you'd expect if you're at work or away for the day.

Plan on at least one roof vent, and ideally a side vent too, even in a smaller 60–80 sq ft greenhouse. An automatic, temperature-triggered opener that works without electricity is a relatively cheap upgrade that makes a real difference on the days you're not around to open things yourself. For larger greenhouses, or if you're growing heat-sensitive seedlings, a circulation fan helps even out the temperature difference between floor and ceiling.

Shading becomes important from late spring onward. A roll-up shade cloth gives you more flexibility than painting panels with shading compound, which is much harder to adjust day to day. Both too much and too little shading cost you yield — too much sun scorches leaves, too little stresses plants more than necessary in peak heat.

Heating for an earlier start or year-round use

If you want to sow and plant several weeks earlier than usual, or keep the greenhouse frost-free through winter, passive solar warmth alone usually isn't enough outside the mildest climates. A simple thermostat-controlled frost protection heater that only switches on just above freezing keeps plants alive without running up your power bill. If you're pushing heat-loving crops like peppers and tomatoes really early, it's usually the combination of good insulation, supplemental heat and grow lights that makes the difference — not the greenhouse alone.

A cheap way to boost insulation is lining the inside walls with large-bubble bubble wrap going into winter or a cold spring month. It cuts light transmission slightly, but noticeably reduces heat loss, and it's easy to take back down once the season allows full light again.

Common mistake. Relying on the door alone for airflow. It moves far less air than a roof vent paired with a low side vent, which together create a natural draft through the structure.

How Much Does a Greenhouse Cost?

The price range is enormous, and brand rarely explains the difference — material, size and whether the price includes a foundation or assembly do.

Budget for the foundation separately if it isn't included — an insulated concrete slab is usually the single biggest add-on cost, often running into the thousands depending on size and whether you hire it out or do it yourself. Running power for heat, a fan or lighting adds the cost of wiring and typically an outdoor-rated outlet.

Good to know. A cheaper greenhouse that gets looked after — condensation wiped down, hinges oiled, a cracked panel replaced promptly — often lasts just as long as a pricier one left to weather untended. Maintenance matters more than the price tag.

Accessories Worth Budgeting For

The structure itself is only half the investment. The right accessories determine whether you actually use it every week or it slowly turns into storage.

Tiered shelving and benches make better use of vertical space than lining pots up on the ground, especially in a smaller greenhouse. A simple drip irrigation system on a timer saves time while you're away and waters more evenly than hand-watering, which crops like tomatoes and chile peppers appreciate. A min/max thermometer tells you how hot and cold it actually gets when you're not there, which is more useful than checking by hand.

Storage space for pots, soil and tools is easy to forget when you're sizing a greenhouse, but it makes a real difference to how practical the space feels to work in over time. If you already have a raised bed in the yard, a greenhouse pairs well alongside it rather than replacing it — the raised bed for crops that handle outdoor conditions, the greenhouse for anything that needs extra warmth and shelter.

How to Choose the Right Greenhouse, Step by Step

1. Decide how you'll actually use it. Mostly starting seedlings and extending the shoulder seasons, or growing heat-loving crops all summer? That shapes both material and size.
2. Measure the spot in your yard. Check sun exposure through the day, distance to property lines, and whether tree shade becomes a problem in summer.
3. Pick a material based on budget and durability. Polycarbonate is the safest compromise for most people, glass if light and appearance matter most, film if you want to test the idea cheaply first.
4. Size it for real use, not just plants. Add walking room and accessories mentally, not just growing area — most people regret going too small, not too big.
5. Check local permit thresholds. Many areas exempt structures under roughly 120–200 sq ft, but confirm with your local building department.
6. Settle on a foundation before you order the greenhouse. The base should ideally be finished or underway before delivery, not figured out afterward.
7. Budget for ventilation and shading. An automatic opener and shade cloth aren't luxuries — they're what determines whether the greenhouse is usable in the middle of summer.
8. Compare total cost, not just the kit price. Foundation, assembly and accessories can easily add as much as the greenhouse itself.

Common Mistakes When Buying a Greenhouse

• Buying too small. Nearly everyone who buys their first greenhouse wishes, in hindsight, they'd gone one size up.
• Skipping the foundation to save money. A greenhouse without a proper base settles, tilts and lets moisture in within the first year.
• Forgetting ventilation. A poorly vented greenhouse can get dangerously hot for seedlings on an ordinary overcast spring day.
• Siting it wherever there's open space. Shade from a tree or wall gives worse results than moving something else in the yard instead.
• Missing local permit thresholds. Building bigger than the exempt size without checking first can turn into an expensive surprise.
• Buying on price instead of intended use. A cheap hoop house asked to perform like a year-round structure won't hold up, no matter how good the deal looked.

Frequently Asked Questions

Which material is best for a greenhouse — glass or polycarbonate?
It depends on your priorities. Glass lets in the most light and lasts for decades but costs more, weighs more and is more vulnerable to impact. Polycarbonate insulates better, weighs less and holds up to knocks, which is why it's the most common choice for home greenhouses. If you're unsure, twin-wall polycarbonate at least 6mm thick is a safe middle ground.

What size greenhouse do I need for an ordinary backyard?
60–80 sq ft (6–8 m²) suits most gardeners who want benches on both sides with room to move comfortably. Size up rather than down where you can — most first-time buyers wish, a year in, that they'd chosen one size larger.

Do I need a permit for my greenhouse?
Many areas exempt small, freestanding, unheated greenhouses — often under roughly 120–200 sq ft in the US or around 100–110 sq ft in Canada — but thresholds vary significantly by city and county. Adding electricity or plumbing often triggers permit requirements regardless of size, so always confirm with your local building department.

Which foundation is best for a greenhouse?
A pier foundation or an insulated concrete slab gives the best stability and heat retention for a permanent structure. If the greenhouse is only staying up for a season or two, a bed of compacted gravel is usually enough, as long as the ground slopes away from the structure rather than toward it.

How much does a greenhouse cost, roughly?
A small hoop house can run $100–$300, while an aluminum-and-polycarbonate kit around 60–80 sq ft typically lands between $300 and $1,500. A glass greenhouse of similar size usually costs $1,500–$5,000, and the foundation is often a separate cost on top of that.

Does a greenhouse need to face south?
A south or southwest orientation gives the most sun and is the best general rule, but a greenhouse that only gets strong morning or midday sun still works well. The main thing is avoiding shade from trees or walls during whatever sun hours you do have.

How do I ventilate a greenhouse so it doesn't overheat?
A roof vent paired with a lower side vent creates a natural draft that moves far more air than opening the door alone. An automatic, temperature-triggered opener helps on the days you're not around to manage ventilation yourself.

Can I put a greenhouse on a lawn without a foundation?
Yes, for a smaller hoop house or seasonal greenhouse that's fine, though a bed of compacted gravel underneath is still worth adding. It keeps weeds down, improves drainage, and stops the floor from turning into a muddy, uneven mess after a single rainy week.

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